The transformation of steroids by microorganisms has been widely studied and documented. Apparently, the earliest such work was by Mamoli and Vercellone in 1937, Ber. 70, 470 and Ber. 70, 2079. They disclosed the reduction of 17-ketosteroids to 17.beta.-hydroxysteroids by fermenting yeast. Since then, Peterson and Murray disclosed the 11.alpha.-hydroxylation of progesterone with the fungus Rhizopus nigricans; see, U.S. Pat. No. 2,602,769 (1952). Kraychy et al. in U.S. Pat. No. 3,684,657 (1972) discloses the selective microbiological degradation of steroidal 17-alkyls by fermenting a steroid containing at least 8 carbons in the 17-alkyl side chain with Mycobacterium sp. NRRL B-3683 to prepare androst-4-ene-3,17-dione (AD), androst-1,4-diene-3,17-dione (ADD), and 20.alpha.-hydroxymethylpregna-1,4-dien-3-one. Marsheck et al. in U.S. Pat. No. 3,759,791 (1973) disclose the selective microbiological preparation of androst-4-ene-3,17-dione by fermenting a steroid of the cholestane or stigmastane series containing at least 8 carbons in the 17 -alkyl side chain with Mycobacterium sp. NRRL B-3805, which has been characterized as Mycobacterium vaccae.
United States application Ser. No. 735,075, now abandoned, discloses a process for preparing predominantly AD using the microorganism M. fortuitum NRRL B-11045. Small amounts of ADD are also produced in the process. This is considered to be the best prior art process for preparing AD.